1. Field of the Invention
This invention is directed to a pelvic alignment assembly designed to be used during a total hip replacement surgery for purposes of accurately positioning a prosthetic acetabular cup in the hip joint socket by reproducing precise anatomical alignment of the pelvis. More in particular, immediately prior to the insertion of the acetabular cup, a surgeon utilizing the pelvic alignment assembly of the present invention can reposition the patient, typically by forward or backward rotation of the patient, and determine when the pelvis has accurately assumed a pre-determined xe2x80x9cbaselinexe2x80x9d or reference position, initially established at the beginning of the surgical procedure, which is substantially indicative of a true lateral position or a true anterior-posterior position of the pelvis, and thereby, optimize the accurate positioning of the acetabular cup within patient""s the hip joint socket.
2. Description of the Related Art
As people age, it is relatively common for there to be some deterioration of the hip joint, and more in particular, of the head of the femur or thigh bone, with the result often being that many such persons will have to undergo a total hip replacement (xe2x80x9cTHRxe2x80x9d) surgery performed by an orthopedic surgeon. A total hip replacement surgery involves the use of a prosthetic femoral component comprised of a stem that fits into the upper femur. On the upper or proximal aspect of the stem is a ball which will function to replace the patient""s damaged or worn out of femoral head. To accommodate placement and positioning of the femoral component within the hip joint, it is necessary to insert a prosthetic acetabular cup to receive the ball-like end of the femoral component in substitution for the socket of the human hip joint. In order to achieve optimum performance of these cooperative prosthetic components, the acetabular cup must be positioned as accurately as possible within the pelvis of the patient. Inaccurate positioning or alignment of the acetabular cup within the hip joint can present extensive and serious problems to the patient after surgery and the requisite healing period, such as providing the patient with a decreased range of motion, the subsequent and possibly accelerated loosening or failure of either or both of the acetabular and femoral components, as well as possible dislocation of the hip joint. Following surgery and progressively over the first year subsequent to surgery, scar tissue normally forms about the inserted prosthetic components, which serves to recreate a hip joint capsule called a pseudocapsule which typically aids in the prevention of hip dislocation. However, when the acetabular cup is oriented in a less than an optimal angular position, hip dislocation is thought to be much more likely even when the patient is performing normal, everyday activities which require the hip joint to pass through a normal range of motion. Hip dislocation is one of the most dreaded complications after THR surgery and it is quite well understood in the medical profession that the most common reason for post-operative total hip dislocation is less than optimally positioned acetabular components, also known as acetabular malposition.
In properly orienting the acetabular cup for receipt of the prosthetic femoral component, it is necessary to accurately establish both the abduction angle as well as the anteversion angle. Typically, the anteversion angle, also known as forward flexion, is generally in the range of about 10 degrees to about 25 degrees. The abduction angle is typically in the range of about 35 degrees to 50 degrees, with a most preferred angle being at or about 45 degrees. Due to the well recognized fact that an improperly positioned acetabular component can subsequently cause the patient numerous problems, as set forth above, a number of devices or instruments have been designed to aid in the proper positioning and/or alignment of the acetabular cup.
These known devices have included cup positioners which comprise a pusher ball that is sized and shaped to fit the recess formed within the acetabular component, along with one or more positioned arms, a positioned flange juxtaposed to the pusher ball and a pusher arm connected to the ball and to the flange, to enable the user to push the acetabular cup, when it is resting on the flange into the patient""s prepared acetabulum during the THR surgery. However, in the utilization of such devices, the pelvis of the patient should have been properly oriented in either a true anterior-posterior or a true lateral position in order to accomplish an optimal, predicted cup position.
There has been, unfortunately, almost a complete lack of devices in the medical field to help with accurately achieving an established pelvic position. This has left the surgeon to estimate, to the best of his or her ability, the position or alignment of the pelvis in order to utilize the known devices or instruments, of the type discussed above, for positioning of the prosthetic acetabular cup within the hip joint. Estimation of the pelvic position, in the manner set forth above, frequently involves only the surgeon""s visual observation of the patient""s orientation in an effort to accomplish the desired pelvic alignment. Such estimations are further encumbered by relatively little of the patient""s body being exposed during surgery because of the sterile surgical drapes covering the patient. As such, it is not uncommon to misjudge the anatomical alignment of the pelvis, particularly where the patient suffers from obesity, congenital abnormalities, or bone and/or soft tissue destruction from previous surgeries.
In addition, there are close tolerances involved in accurately establishing both the anteversion angle and the abduction angle, discussed above. Therefore, the use of known devices of the type set forth above, or the unintentional failure to accurately determine the anatomical alignment of the pelvis in a true anterior-posterior or true lateral position, may very well result in the acetabular component being improperly positioned when implanted into the pelvis of the patient.
Accordingly, there is a long felt need in the medical field for reliable, medical instrumentation which would be capable of accurately establishing a proper or preferred anatomical position of a patient""s pelvis, which may be defined to mean a true anterior-posterior position or a true lateral position of the pelvis during a THR surgery. More in particular, prior to the implantation of the acetabular cup into the patient""s pelvis, the pelvis should be repositioned into a predetermined position in order to optimally implant and orient the acetabular component related to the prosthetic femoral component. As discussed above, implementation of the acetabular cup is optimally accomplished if the pelvis of the patient is properly oriented in either a true anterior-posterior or a true lateral position. If an alignment assembly were developed to properly re-orient the patient in such a position, it would greatly enhance the surgeon""s ability to optimally and reproducibly position the acetabular cup. The patient would be more likely to function through a normal range of movement, with a greatly decreased fear of either hip dislocation or accelerated deterioration of the implanted prosthetic components. If any such alignment assembly were developed, it would preferably include a visually observable instrument structured to facilitate the establishment and/or re-establishment of a baseline or reference position of the pelvis, when in its normal or proper anatomical alignment defined by a true anterior-posterior position or true lateral position. More specifically, any such alignment assembly should be structured so as to be capable of being adjustably oriented or positioned to reestablish the aforementioned baseline or reference position, indicative of proper pelvic alignment of the patient, and thereby, to more reliably assure the accurate placement of the acetabular cup.
The present invention is designed to address these and other needs which remain in the art and comprises an alignment assembly, The alignment assembly of the present invention is designed to assist with the accurate positioning of a prosthetic acetabular cup into the pelvis of a patient during a total hip replacement (THR) surgery. More specifically, the alignment assembly of the present invention allows the surgeon to accurately orient the pelvis by repositioning it into a previously established or baseline position of proper anatomical alignment, wherein the patient is positioned in a true anterior-posterior or a true lateral position, depending on the surgical approach which the surgeon elects to use.
In at least one preferred embodiment the alignment assembly of the present invention comprises an elongated pin such as, but not limited to, a Steinmann pin. The distal end of the elongated pin is specifically structured to be anchored into the pelvis so as to extend outwardly therefrom. The alignment assembly further comprises a base removably mounted on the opposite, outwardly extending, proximal end of the elongated pin, with the base being movably connected to a mounting member. The mounting member includes a socket dimensioned and configured to removably receive the outwardly extending, proximal end of the elongated pin therein, so as to allow stable but removable support and attachment of the base to the elongated pin.
The alignment assembly additionally comprises an adjustment assembly, which is mounted at least in part on the base and which is at least partially interconnected to the mounting member. The adjustment assembly is specifically designed to be accessed from the exterior of the base by being manipulated by the surgeon or other medical personnel. Selective adjustment of the relative positions between the base and the mounting member is thereby accomplished, as will be explained in greater detail hereinafter.
The alignment assembly additionally includes a visually observable instrument or orientation indicator structured to facilitate the establishment and/or re-establishment of a baseline or reference position of the patient""s pelvis in a normal or proper anatomical alignment defined by a true anterior-posterior position or true lateral position. The visually observable instrument or orientation indicator preferably, but not necessarily, comprises a level structure in the form of a xe2x80x9cbubble-typexe2x80x9d of level secured to the base and moveable therewith. Further, the level structure is disposed on the base in a position which is readily observable by the surgeon and/or other medical personnel, while the base is supported on the proximal end of the pin, due to the interconnecting disposition of the mounting member, as generally set forth above.
It is emphasized that while the preferred embodiment comprises the orientation indicator in the form of a bubble type level, a variety of other indicators could be utilized. Such additional orientation indicators would preferably be visually observable and include electrical, digital and/or mechanical structures which sense and clearly indicate a proper orientation of the base. The aforementioned baseline or reference position indicative of the patient""s pelvis being disposed in a normal or proper anatomical alignment would thereby be established.
In addition, the base of the alignment assembly particularly when using a level structure, preferably includes a locking assembly that is operatively connected to the mounting member as well as the base in a manner which is capable of being selectively positioned in either a locked or an unlocked position. The locked position prevents or significantly restricts movement between the base and the mounting member, thereby preventing operation of the adjustment assembly for purposes of changing the position of the base relative to the mounting member. With the locking assembly disposed in the locked position, the surgeon is reasonably assured that the intended position of the level structure relative to the elongated pin may be re-established, when necessary to accomplish the predetermined established anatomical alignment of the pelvis, immediately prior to insertion of the acetabular cup. Further, proper use and observation of the level structure or other orientation indicator allows the surgeon to reestablish the required pelvic alignment through minimal physical manipulation or repositioning of the patient, immediately prior to the insertion of the acetabular cup into the pelvis.
In one preferred embodiment, use of the alignment assembly of the present invention during a THR surgery involves positioning the patient into a true anterior-posterior or true lateral position on the operating table. After appropriate preparation and draping of the patient, the distal end of the elongated Steinmann pin is anchored to the iliac crest of the patient""s pelvis. Initial alignment of the pelvis is accomplished by orienting the elongated pin in an approximately perpendicular relation to the floor, ground or other supporting surface. The base, being movably connected to the mounting member, is supported on the pin by attaching the mounting member to the outwardly extending or proximal end of the pin. While the base remains supported on the pin, the adjustment assembly is manipulated by the surgeon or other medical personnel until the level structure, fixedly secured to the base and movable therewith, indicates that it is oriented into a true horizontal or other applicable reference position. The locking assembly is then manipulated into the locked position, thereby assuring a relative fixed orientation of the level structure relative to the pin, when the base is mounted thereon. The base, along with the mounting member and the level structure, can then be removed from the outwardly extending end of the pin, while the distal end of the pin remains anchored into the pelvis. The surgical procedure associated with a total hip replacement or THR then proceeds to the point where the acetabular cup is ready for insertion into the hip joint socket of the pelvis. Immediately prior to the insertion of the acetabular cup, the base is again supported on the elongated pin by reattaching the mounting member to the proximal end. The locking assembly still maintains the level in its previously, predetermined fixed position relative to the pin. Accordingly, in order to re-orient or position the level structure into the true horizontal or established reference orientation, which was established by locking the mounting member to the base, the patient is then physically moved, such as by rotating the patient, preferably forward or backward, to once again orient the level structure in the predetermined, initially established baseline or reference position. Visual observation of the level structure indicates to the surgeon or other medical personnel, such as when the preferred xe2x80x9cbubblexe2x80x9d is appropriately located or xe2x80x9ccenteredxe2x80x9d within the level structure, that the level structure, the elongated pin and accordingly, the pelvis is re-oriented in the same, pre-determined established anatomical alignment for optimizing the accurate positioning and insertion of acetabular cup.
The objects and features of the present invention set forth above are intended to be illustrative only and should not be construed as limiting in any way. In fact, these and other objects, features and advantages associated with the present invention should become more evident from the drawings and the detailed description of the preferred embodiments for the invention, which follow.